Hydrogen is attractive and has been used as the fuel in many types of devices, such as: in fuel cells for producing electricity, in combustion engines, including rockets or internal combustion engines, and in chemical processing devices, including those used in the refining of metallic components. Typically hydrogen, or more particularly, hydrogen enriched gas, is processed from methanol, natural gas, petroleum, or ammonia using a chemical reactor, typically called a hydrogen generator or reformer. A reformed hydrogen fuel cell (RHFC), utilizes hydrogen enriched gas processed from liquid or gaseous hydrocarbon fuels, such as methanol, using a fuel reformer.
Methanol is the preferred fuel for use in fuel reformers, or hydrogen generators, because methanol is easier to reform into hydrogen enriched gas at a relatively low temperature and yields a minimum number of gaseous by-products (carbon dioxide and carbon monoxide) compared to other hydrocarbon fuels such as natural gas, ethanol, petroleum, gasoline, or butane. This is especially important for small portable units, where the temperature of the reformer unit would be a concern. The reforming or converting of methanol into hydrogen enriched gas usually is accomplished using one of three different types of reforming processes. These three types are steam reforming, partial oxidation reforming, and autothermal reforming. Of these types, steam reforming is the preferred process for methanol reforming because it is the easiest to control, yields the minimum number of gaseous by-products (carbon dioxide and carbon monoxide), and produces a higher hydrogen output, at a lower temperature, thus lending itself to favored use. During steam reforming, raw methanol is catalytically converted, in the presence of water and with the application of heat, to a hydrogen enriched gas. Although, steam reforming is the preferred process, partial oxidation reforming and autothermal reforming are utilized in many instances. During partial oxidation reforming, raw methanol is converted to a hydrogen enriched gas through partial oxidation of methanol over a catalyst in a limited supply of oxygen or air to prevent complete oxidation. Since this is an exothermic reaction, it does not require heat input to proceed. The reaction will proceed without any additional heat input provided the methanol and oxygen are in contact with the proper catalyst. Control of oxygen partial pressure and temperature is very critical, and for portable methanol reforming, the higher operating temperature of the reformer is a concern.
Autothermal reforming is a combination of the catalytic partial oxidation and steam reforming process. During the autothermal methanol reforming process, the partial oxidation reaction which produces heat is carefully managed to provide sufficient heat for the steam reforming reaction. In an autothermal reformer, the reactions between the input reactants, namely the methanol, water and air (or O2), are carefully balanced over the catalyst, to produce CO2 and H2 gases with minimum amount of CO. The partial oxidation step and steam reforming step may be done in the same or separate compartments during autothermal reforming.
Fuel reformers have been developed for use in conjunction with many new devices, including fuel cell devices. Many of these fuel cell devices include reformers which are typically cumbersome and complex devices consisting of several discrete sections connected together with gas plumbing and hardware to produce hydrogen gas. Accordingly, reformers have not been found suitable for portable power source applications, or in other applications requiring minimal size and weight. To date, no fuel reformer has been developed utilizing ceramic monolithic structures in which the miniaturization of the reformer has been achieved. Laminated ceramic components containing miniature channels and other features which utilize low pressure lamination ceramic technology, are now commonly being developed for use in microfluidic management systems. Monolithic structures formed of these laminated ceramic components provide for three-dimensional structures that are inert and stable to chemical reactions and capable of tolerating high temperatures as well as providing for miniaturized structures, with a high degree of electronic circuitry or components embedded or integrated into such a ceramic structure for system control and functionality. Additionally, the ceramic materials used to form ceramic devices, which have microchannels formed within the structure, are considered to be excellent candidates for catalyst supports in microreactor devices for generating hydrogen for supplying miniaturized fuel cells.
Accordingly, it is an object of the present invention to provide for a miniaturized hydrogen generator, or fuel processor, that provides for the reforming of a fuel to a hydrogen enriched gas.
It is yet another object of the present invention to provide for a monolithic structure for the reforming of a fuel to a hydrogen enriched gas.
It is still another object of the present invention to provide for a monolithic structure that is formed by utilizing ceramic technology, thereby providing for the integration of a plurality of internal plumbing interconnections and electrical circuitry and connections.
It is another object of the present invention to provide for a hydrogen generator, or fuel processor, that is miniaturized for use in conjunction with: (i) fuel cells for portable device applications; (ii) combustion devices; (iii) chemical processing devices; and (iv) other devices in which hydrogen enriched gas is consumed as fuel.